This research program focuses on the interaction of DNA and RNA tumor virus proteins with specific components of the host cell. The members of the program represent a range of disciplines from biology through physical chemistry and share the conviction that tumor virus proteins can be used to identify an event or chain of events important to the understanding of cancer at the molecular level. Studies in six related areas are described: I. Adenovirus DNA-binding protein; II. Interactions between the RNA tumor virus Src protein with cellular proteins; III. Cellular tumor antigens; IV. Adenovirus early gene expression; V. Interactions between the SV40 A protein and simian RNA polymerase II, and VI. Host cell components in poliovirus genome replication.